There has been mounting frustration among the Obama administration and the military’s top leadership over China’s failure to do something, anything, about the North Korean lunacy; that frustration is now publicly coming out in the wake of the North’s sinking of the South Korean ship Cheonan and the sound of crickets from Beijing.

Last night, speaking at the Asia Society dinner in Washington, DC, Joint Chiefs chair Adm. Mike Mullen said he was “dismayed” at Beijing’s failure to put any real pressure on North Korea.

Then Mullen went further, questioning the motives behind China’s military modernization:

“[T]heir heavy investments of late in modern, expeditionary maritime and air capabilities seems oddly out of step with their stated goal of territorial defense. Every nation has a right to defend itself, and to spend as it sees fit for that purpose. But a gap as wide as what seems to be forming between China's stated intent and its military programs leaves me more than curious about the end result. Indeed, I have moved from being curious to being genuinely concerned."

Defense Secretary Robert Gates has also upped the rhetoric on Chinese military adventurism in Asia. We linked to this International Institute for Strategic Studies (IISS) brief on recent, and aggressive, PLA Navy operations and exercises in the South China Sea which territorial and fishing disputes with Vietnam. On a number of occasions, PLA ships have seized Vietnamese fishermen.

Gates doesn’t like what he sees. Two years ago, while speaking at the International Institute for Strategic Studies in Singapore, Gates had this to say about freedom of movement in the South China Sea:

“[W]e welcomed back in the mid-1990s moves toward a “code of conduct” among states with competing territorial and resource claims in South China Sea. We stressed then, as we do today, that we do not favor one claim, or one claimant country, over another. We urged then, as we do today, the maintenance of a calm and non-assertive environment in which contending claims may be discussed and, if possible, resolved. All of us in Asia must ensure that our actions are not seen as pressure tactics, even when they coexist beside outward displays of cooperation.”

Compare those comments to what Gates said at the same venue, IISS, in the same locale, Singapore, just last week:

“[T]he South China Sea is an area of growing concern. This sea is not only vital to those directly bordering it, but to all nations with economic and security interests in Asia. Our policy is clear: it is essential that stability, freedom of navigation, and free and unhindered economic development be maintained. We do not take sides on any competing sovereignty claims, but we do oppose the use of force and actions that hinder freedom of navigation. We object to any effort to intimidate U.S. corporations or those of any nation engaged in legitimate economic activity.”

Might not seem like much, but in diplomatic messaging terms between great powers, there are lines being publicly drawn.